1. Field of the Invention
The present invention relates to a manufacturing method of a single crystal and an apparatus of manufacturing the same, more particularly to a horizontal magnetic field applied CZ method (hereinafter referred to as a HMCZ method) wherein while applying a horizontal magnetic field to a raw material melt in a crucible with a magnetic field application apparatus, a single crystal is pulled from the melt, and an apparatus suitable for carrying out this manufacturing method.
2. Description of the Prior Art
It has been well known that the foregoing HMCZ method is superior to an ordinary Czochralski method (hereinafter referred to as a CZ method) in various respects. An apparatus used for the execution of the HMCZ method is an improvement of the apparatus used in the ordinary CZ method, wherein a pair of magnetic field application apparatuses, each comprising an electromagnet such as a superconductive magnet, are disposed facing each other interposing a crucible in the outside of a heater for heating the crucible.
When a silicon single crystal is, for example, pulled from a silicon melt in a quartz crucible, the thermal convection of the silicon melt is suppressed according to the HMCZ method, and the fluctuations of a temperature with time in the surface portion of silicon melt (temperature of interface between solid and liquid) is greatly reduced, and, at the same time, a dissolution amount of SiO from the crucible is reduced. As a result, the generation of defects and dislocations is suppressed, and, moreover, the silicon single crystal with uniformity and low oxygen concentration can be easily obtained.
U.S. Pat. No. 4,565,671 discloses an example of a single crystal manufacturing apparatus using the HMCZ method. This apparatus is designed such that the central axis of a superconductive coil is in accord with the surface of the melt in the quartz crucible so that the thermal convection near the surface of the melt is suppressed and the thermal convection area is formed below the vicinity of the surface of the melt.
In this apparatus, the heat transfer to the interface layer between the single crystal during being pulled and the melt is enhanced so that the temperature difference between the crucible periphery and the aforementioned interface layer can be reduced. At the same time, the melt which is fully agitated below the vicinity of the surface thereof, is supplied to the aforementioned interface. Therefore, the single crystal with the more uniform property compared to that obtained by the apparatus according to the ordinary CZ method can be grown. In addition, the crack of the crucible produced by thermal stress can be prevented.
There are two subjects to be solved on the single crystal growth technique required for the recent single crystal, especially for silicon single crystal, of a large diameter. One is a low oxygen concentration, and the other is an increase in productivity owing to a stable crystal growth. Recent years, the device manufacturing processes have been conducted in cleaner environment than before so that the necessity for the gettering effect for heavy metal impurities within the wafer is lessened. Therefore, the demand for a single crystal of a low oxygen concentration has been increased.
However, as the diameter of the single crystal becomes larger, the diameter of the quartz crucible used for the growth the single crystal becomes larger. As a result, the dissolution amount of the inner surface layer of the crucible to the melt in the crucible increases so that the oxygen concentration in the melt becomes higher. Thus, the oxygen concentration in the single crystal of a large diameter is liable to be high compared to that of a small diameter obtained by a small-sized crucible.
As factors that the dissolution amount of the quartz crucible inner surface into the melt increases as the diameter of the single crystal becomes larger, (a) the increase in a friction force, when the crucible rotates, due to the tendency of the weight of the melt to grow larger, (b) the increase in the heating amount required for heating the crucible accompanied with the tendency of the crucible diameter to grow larger, and (c) the increase in the melt convection in the melt due to the increase of temperature difference in the melt are given. Therefore, to reduce the oxygen concentration in the single crystal of a large diameter, it is very essential to suppress the convection of the melt in the crucible.
In the manufacturing apparatus of the single crystal disclosed in the foregoing United States Patent, however, the uniformity of the horizontal magnetic field applied to the melt is not necessarily satisfactory. Therefore, the suppression effect on the melt convection in the crucible is not necessarily sufficient. For this reason, when the silicon single crystal of the diameter larger than 8 inch is pulled, there has been a drawback that it is difficult to obtain the product with an uniformly low oxygen concentration and less defects.
Furthermore, in the manufacturing apparatus of the single crystal disclosed in the foregoing United States Patent, though the convection in the vicinity of the surface of the melt in the crucible is suppressed, the apparatus is designed such that the thermal convection under the vicinity of the surface is present. Therefore, the convection at the lower portion of the crucible is large likewise the conventional apparatus, so that the dissolution and corrosion of the quartz crucible proceed excessively and the lifetime of the crucible is shortened.